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Bug #48484 array_product(array()) returns 0 instead of 1
Submitted: 2009-06-06 11:22 UTC Modified: 2010-12-12 20:27 UTC
From: zhalassy at loginet dot hu Assigned: iliaa (profile)
Status: Closed Package: Math related
PHP Version: 5.2.9 OS: *
Private report: No CVE-ID: None
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 [2009-06-06 11:22 UTC] zhalassy at loginet dot hu 
Description:
------------
array_product(array()) returns 0 instead of 1. Empty product is 1 (hence "1" is neutral in multiplication) in mathematics.

Example:

array_product(array(1,2)) * array_product(array(3,4)) === /* should be */ array_product(array()) * array_product(array(1,2,3,4));

example implementation:

function array_product($array){
    $product = 1;
    foreach($array as $element) $product *= $element;
    return $product;
}


Reproduce code:
---------------
echo product_array(array());

Expected result:
----------------
It should return 1.

Actual result:
--------------
It returns 0.

Patches

Pull Requests

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 [2009-06-06 11:34 UTC] zhalassy at loginet dot hu 
http://en.wikipedia.org/wiki/Identity_element

An identity with respect to addition is called an additive identity (often denoted as 0) and an identity with respect to multiplication is called a multiplicative identity (often denoted as 1). The distinction is used most often for sets that support both binary operations, such as rings. The multiplicative identity is often called the unit [...]

http://en.wikipedia.org/wiki/Unital

In mathematics, an algebra is unital (some authors say unitary) if it contains a multiplicative identity element (or unit), i.e. an element 1 with the property 1x = x1 = x for all elements x of the algebra.

http://en.wikipedia.org/wiki/Empty_product
 [2009-06-09 02:21 UTC] scottmac@php.net 
The current behavior was set in bug #35014, pretty sure we should change it as you suggest.

Confirming for now.
 [2009-10-13 05:33 UTC] chrisstocktonaz at gmail dot com 
Patch is of course trivial, posting it only to have no unassigned math bugs!

Index: ext/standard/array.c
===================================================================
--- ext/standard/array.c	(revision 289602)
+++ ext/standard/array.c	(working copy)
@@ -4020,7 +4020,7 @@
 	}
 
 	if (!zend_hash_num_elements(Z_ARRVAL_P(input))) {
-		RETURN_LONG(0);
+		RETURN_LONG(1);
 	}
 	ZVAL_LONG(return_value, 1);
 [2010-12-12 20:27 UTC] iliaa@php.net 
Automatic comment from SVN on behalf of iliaa
Revision: http://svn.php.net/viewvc/?view=revision&revision=306288
Log: Fixed bug 48484 (array_product() always returns 0 for an empty array).
 [2010-12-12 20:27 UTC] iliaa@php.net
-Status: Verified +Status: Closed -Assigned To: +Assigned To: iliaa
 [2010-12-12 20:27 UTC] iliaa@php.net 
This bug has been fixed in SVN.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
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